A turbine rotor is used as a rotated body in, for example, a steam turbine, a gas turbine, and a power generation plant applied to a combined cycle including a combination thereof. If the turbine rotor is left in a stopped state with high temperature after operation, the turbine rotor may be bent, in some cases, due to thermal distortion of the turbine rotor caused by temperature difference in a turbine casing along with temperature decrease of the steam or the gas inside a turbine, or due to own weight of the rotor.
Accordingly, to prevent the turbine rotor from being bent, it is necessary to perform turning in which the turbine rotor is rotated at a low speed for a predetermined time during the operation stop of the steam turbine, or the like. A turning device that rotates the turbine rotor by power of a motor is widely used to perform such turning.
The turning device has been subjected to various improvements for prevention of breakage and delay of deterioration with time. For example, Patent Literature 1 discloses a turning device including a reverse rotation preventing unit at a shaft end of a pinion shaft. The reverse rotation preventing unit prevents reverse rotation of the pinion shaft and a one-way clutch that transmits rotating force of the turning motor to the pinion shaft, in order to prevent the turning device from being reversely rotated and being damaged when the turbine rotor is reversely rotated.